bug#8682: 24.0.50; doc strings of `isearch-mode', `isearch-forward', etc.

[Drew Adams]

> > The bug is about undocumented parameters, poorly documented 
> > parameters,
> 
> Sure.  Please send us a suggested patch,

I don't know what the info about the functions and parameters etc. should be.
That's why I'm asking for real doc strings.

Someone familiar with this code should be able to supply the necessary info.  If
you then need help with wording (unlikely), I can try to help.  It is the info
content that is missing/incomplete/unclear.